The present invention relates to a method for manufacturing various types of containers made of synthetic resin (hereinafter referred to as "synthetic resin container(s)") and, more particularly, to a method capable of easily manufacturing synthetic resin containers having excellent strength and heat insulating characteristics such as a wash basin, wash or kitchen sink and bathtub.
Hitherto, the most prevailing synthetic resin containers such as bathtubs and sinks have been manufactured by an FRP manufacturing method. Specifically, a bathtub or the like is formed of a material mainly containing fiberglass reinforced polyester resin.
The following problems have recently been highlighted with regard to bathtubs of such type and the like containers.
(1) The use of glass fiber deleteriously affects the working environment. Specifically, glass fiber clings to operator's clothing or sticks into operator's skin. Further, minute glass fiber fragments are sucked into the operator's body together with air breathed in and hence cause various health hazards. PA1 (2) It is difficult to recycle the material of a product since the material is a thermosetting resin and, furthermore, glass fiber is used therein. PA1 (a) forming an inner surface layer component adapted to constitute an inner surface of the container from a synthetic resin sheet by thermoforming; PA1 (b) fitting the inner surface layer component onto a male die; PA1 (c) pouring a synthetic resin in a melt condition into the inside of a female die; PA1 (d) fitting the male die onto the female die and bringing the male die close to the female die to compress the synthetic resin, thereby compressively extending the synthetic resin within a cavity defined between a back surface of the inner surface layer component fitted on the male die and the female die; PA1 (e) injecting compressed air into the synthetic resin through at least one air nozzle formed in the female die while enlarging a gap between the male and female dies so as to correspond to a predetermined thickness of a prospective molded product, thereby forming hollow portions within the synthetic resin; PA1 (f) causing the compressed air to press the synthetic resin against entire inner surface of the cavity defined between the back surface of the inner surface layer component and the female die; and PA1 (g) cooling the synthetic resin to solidify the same and releasing a molded product from the dies.
While the recycling of materials of products is now being advocated all over the world as a part of the environmental protection, ships made of FRP or like products present critical problems because of their large size. Containers such as bathtubs and sinks also face these problems inevitably. Nevertheless, the conventional containers like bathtubs are not able to cope with such problems.
It is a long time since a bathtub made by thermoforming an acrylic resin plate appeared on market. Initially, the bathtub of such type was manufactured from an acrylic plate of about 8 to about 10 mm thickness. This type of bathtub deteriorated with lapse of years and was often damaged by a mere fail-down of a hand shower (a shower tool to be held by hand for use) or the like after being used for only a few years.
In view of such disadvantage, there has recently appeared a bathtub of the type made by thermoforming an acrylic resin sheet of about 5 mm thickness and then reinforcing it with a backup of FRP. It is, however, apparent with this bathtub that again there arise the aforementioned problems (1) and (2) associated with the bathtubs of FRP, a problem of high costs and a like problem.
Furthermore, any of the aforementioned methods necessarily leads to a container product having solid and rather thin wall (around 5 mm in thickness) consisting of single or double layer(s). Hence, it is hard to say that containers requiring a heat insulating function such as a bathtub exhibit heat insulation sufficient to meet the requirements of users.
In view of the foregoing problems, it is an object of the present invention to provide a method for manufacturing synthetic resin containers of a multilayered structure comprising a reinforcing layer which is excellent in both strength and toughness and has a good heat insulating function, and an inner surface layer component which is very agreeable to the touch.